How Old is San Francisco Bay?

In the year 1597, Sir Frances Drake did not discover San Francisco Bay. He did find Drake's Bay, a rather small cove near Point Reyes. He landed his ship for overhaul and spent more than a month exploring the neighborhood. The natives were friendly, since they yet failed to realize the scope of the disaster which Drake's appearance meant to them.

Drake spent weeks looking over the property in Marin County. He probably climbed part way up Mount Tamalpais, and may have visited Tiburon. He still couldn't find San Francisco Bay. Why not?

I have been perusing a book titled California, a Personal History, by Gertrude Atherton, first published in 1914. One of the fun things about reading old books (which maybe no one else has read for the past hundred years) is that you often find intriguing stories that got left out of all the official history text books.

Gertrude suggests that maybe Drake couldn't find the Bay because it wasn't there yet!

Enter Gaspar de Portola, some two hundred years later. To him went the credit of discovering San Francisco Bay, in the year 1769. The Ohlone natives were still friendly. Here I quote from Gertrude Atherton:

"From them he heard the tradition that some two hundred years earlier the space covered by the great inland sheet of water had been a valley, fertile and beautiful, broken by hills and watered by two rivers that rose in the far north and found their outlet to the sea through Lake Merced. Then came a mighty earthquake, the valley sank, the hills of the coast were rent apart, the salt waters rushed in and covered not only the sunken valley floor, but all save the tips of the hills."

As evidence of this startling claim, Atherton points out that ancient shell mounds have been discovered beneath the waters of the Bay. As reference for this statement, she quotes a geologist, James Perrin Smith, writing in Science magazine for September 10, 1909. In former times, up until a hundred years ago, these shell mounds were found all around the Bay Area, some of them covering acres of land and some carbon dated to more than five thousand years ago. Regrettably, the vast majority of these mounds were destroyed for building projects during the last century.

However, there is another piece to this puzzle which was not known to Ms Atherton: Recent carbon dating in the East Bay indicates most of the mounds were abandoned between 700 and 1100 A.D. (This according to Kent Lightfoot, archeologist.) After 1100 they began to be reoccupied, but not nearly to the same degree. It appears they were also put to somewhat different uses, such as burial grounds and village sites. What happened in 700 A.D.? Was there some natural disaster which nearly wiped out the native population? This was about the same time as a "little ice age" that drove the Vikings out of Greenland.

When Gaspar de Portola spoke with the Ohlone, he learned that these vast shell mounds had already been abandoned for a second time, perhaps for hundreds of years.

Is it possible that the native story of the great earthquake which created the Bay may be true? Gertrude Atherton cites several other examples of great quakes in the historic past: The New Madrid quakes of 1911/12, which changed the course of the Mississippi River, the eruption of Krakatoa in 1883, and the Indian earthquake of 1762. If she were writing today, Atherton might well have added the Fukushima earthquake of 2011, which moved the entire island of Japan by several yards.

Here is a description of the India disaster, from an academic journal:

Let us look into the next recorded major earthquake of 2nd April 1762. A very destructive and violent earthquake felt all over Bengal and Arakan (Burma); Chittagong suffered very severely; great explosions heard and opening in the earth formed with water spouted like fountain; earth continued to sink day by day; 60 sq miles permanently submerged;

two volcanoes (mud volcano) said to have opened on the Sita Kunda hills; in Calcutta water tank rose by 6 feet (1.8 m; seiches); at Ghirotty (Gorhatty), 18 miles (28 km) above Calcutta river rose more than 6 feet(1 . 8 m ); at Dacca water rose so suddenly as to carry up hundreds of boats, and many lives were lost. Captain Halsted visited coastal Arakan for survey work in 1841. He documented several uplifted coastal area (13 feet at Terribles; 22 feet at northwest of Cheduba; 9 feet at Foul island etc.) that have been related to the earthquake.



In this case, there were 60 square miles of land "permanently submerged," while other areas were elevated by as much as 22 feet. If the story about San Francisco Bay is true, it means that approximately 200 square miles were submerged.

Is such a cataclysm possible? Certainly it is. A similar catastrophe occurred in prehistoric times, when the island of Santorini blew up, destroying the Minoan civilization. Oddly enough, conventional geology recognizes that the San Francisco Bay was at one time a valley with two rivers flowing through it--but that was back during the last Ice Age, more than 20,000 years ago, when the coastline lay out beyond what is now the Farallone Islands. Academic science recognizes the possibility of great change, as long as it happened a long time ago. That it might have happened in the 16th or 17th Century with no one noticing is unthinkable.

Or is it? Certainly the Ohlone and other nearby tribes would have noticed. In fact they reported  it to Portola. When Drake landed in California, the Pilgrims had yet to dream of landing in New England. The nearest European colony was in Mexico City. Mexicans probably would have felt the quake, but quakes are commonplace there.

Is there any way to prove or disprove this theory? Not being a geologist, I couldn't say. I'm reminded of an old "Peanuts" cartoon. Lucy says to Linus, "I have a theory that Beethoven would have written better music if he had been married." Linus asks, "Is there any way to prove that theory?" To which Lucy responds, "The best theory is one that can be neither proved nor disproved."

Lucy was probably right. However, I would suggest another reason why academic geology will not address this problem: Because if the story turned out to be true, it could scare people.

If such a cataclysm happened once, it could happen again.




This is in the way of a footnote to “How old is San Francisco Bay?” When I originally put forth this theory one of the legitimate objections raised was that there is no evidence today that Lake Merced ever had a direct outlet to the sea, as was claimed in the old Indian legends. There was also skepticism that this area might ever have seen such sudden geological changes.


I have been perusing a remarkable book titled The Annals of San Francisco. This book was published in 1855: The authors were Frank Soule, John H. Gihon, and James Nisbet. Digital versions are freely available at The book gives a blow-by-blow history of the city, from Sir Francis Drake until 1854. For the entry under the year 1852 I discovered the following:



November 23d.—The waters of Lake La Mercede, in the vicinity of the city, and which cover several hundred acres, sank about thirty feet. Shortly before midnight of this day, a shock like that of an earthquake was felt by parties residing near the place; and the following morning it was discovered that a great channel between the lake and the sea had been opened, through a broad and high sand bank, during the night, by which the waters had found a way and been discharged. It was supposed by some, either that the bed of the lake had been suddenly uplifted, by volcanic agency, whereby the raised waters scooped through the yielding bank the channel just mentioned, and that afterwards the bed of the lake had fallen to its former level, or else that a great sinking of the bank itself had taken place (supposed to have been produced by subterranean causes), owing to which depression, the water had been drawn off to the extent mentioned. The most probable conjecture is, that the excessive rains of the season had simply forced open a passage through the broad and loose sand-bank from the lake to the ocean. Formerly the lake had no visible outlet whatever; and its waters had insensibly been kept about the same level by means of evaporation, or by concealed underground communications with the sea.